1. Field of the Invention
The present invention relates to a decompression device for an engine that changes the opening and closing movement of engine valves to decrease the pressure in a combustion chamber while starting the engine.
2. Description of the Related Art
Conventionally, a small four-cycle engine for use in a generator or another device has one or more cylinders. A piston is located inside a cylinder, and the piston and the cylinder define a combustion chamber. The engine also includes an intake port to supply air and fuel to the combustion chamber and an exhaust port to allow exhaust gases to exist the combustion chamber. The intake port and exhaust port are opened and closed by an intake valve and an exhaust valve, respectively. When the air and fuel mixture is ignited in the combustion chamber, the piston is driven toward a crankcase chamber of the engine. The reciprocal movement of the piston rotates the crankshaft. A cam gear, which is driven by the crankshaft, operates to actuate the engine valves, i.e., the intake and exhaust valves, at the proper time.
The engine is typically started by quickly pulling a rope of a recoil starter. One end of the rope is coupled with the crankshaft and the other end has a knob that is accessible from outside the engine. When an operator pulls the knob the rope drives the crankshaft and the engine starts. However, to turn the crankshaft, the piston must be forced against the pressure in the combustion chamber. When the intake and exhaust valves are closed, the pressure in the combustion chamber is high as the piston moves toward its top dead center position. The user then is required to exert a large amount of force to turn the crankshaft and overcome the pressure in the combustion chamber. Consequently, many users are unable to generate the force required to start the engine.
To facilitate the starting of the engine, decompression devices have been proposed that reduce the amount of pressure in the combustion chamber by delaying the closing of the engine valves thereby reducing the force required to start the engine. Decompression levers have been used in some engines to open intake or exhaust valves and thus provide the reduction in pressure needed to start the engine. Examples of such levers are disclosed in JP-B-H06-006889, JP-A-H09-184410, JP-A-H10-159524, U.S. Pat. No. 5,943,992, JP-A-H10-299626, JP-A-H11-081948, and JP-A-H11-081949. These levers typically rotate out of position after starting the engine so that the engine valves open and close normally.
Some decompression levers include multiple parts or complicated geometry that make manufacturing of the levers difficult and expensive. Size constraints, strength requirements, and precise cooperation with other engine components have resulted in decompression devices that are costly and time consuming to manufacture.